US2076489A - Method of providing and forming a gravel pack about well screens in wells - Google Patents

Description

R 1 HI -WM Wi'ml til-MUM Inven. or-z' Howard QWilliar-ns Attorneys.

Patented Apr. 6, 1937 UNITED STATES PATENT OFFICE METHOD OF PROVIDING AND FORMING A GRAVEL PACK ABOUT WELL SCREENS IN WELLS Howard 0. Williams, Minneapolis, Minn., assignor to Edward E. Johnson, Incorporated, St. Paul,

Minn.

Application February 11, 1936, Serial No. 63,374

2 Claims.

My invention relates to a method of providing and forming a gravel pack about well-screens in wells. In the practice of sinking wells, particularly where they serve the purpose of giving a supply of water, the main well casing is sunk through the overlying drift or formations into a stratum carrying the water supply to a sufficient distance to set the well-screen which it is proposed to employ entirely in this water-bearing stratum. The length of the well casing will thus be determined by the thickness of the overlying drift and the depth into the water-bearing stratum to which the well screen may be sunk. The diameter of the main well casing will be a selected diameter sufficiently greater than that of the well-screen to permit the latter to be dropped down through the casing already sunk to a point approximating the bottom of the screen when set, and after that the casing will be raised outside of the well-screen leaving the latter set in position in the water-bearing stratum. Or in some cases the well-screen may be integral with the casing.

Developing the well consists in pumping water therefrom as long as it carries sand, and in performing other well-known steps to cause free sand to be withdrawn and a gravel pack to form about the walls of the well-screen. In doing this, sand and other materials fine enough to pass through said slot openings pass out with the water until the gravel pack about the well screen is set and becomes stable. In certain cases the water-bearing stratum consists principally or entirely of such fine particles without a sufiicient amount of gravel and coarse particles to form a suitable gravel pack around the well screen. In such cases a proper development of the well with a suitable gravel pack about the well screen cannot be obtained by continued pumping of water therefrom, o-r pumping with known assisting processes. Sand will continue to come with the Water and ultimately so much material will be removed that the ground about the wall may sink and cave in and the well be destroyed.

In prior practice attempts have been made to remedy this difliculty by putting down one or more pipes around the well casing, the bottom of said pipe or pipes reaching the area adjacent the well-screen walls, and feeding sized gravel down by gravity thIOLEh the annular opening between the'well casing and this pipe, or separately through these pipes, so, as sand is withdrawn, this sized gravel flows in to take up the space previously occupied by the sand, and finally forms a gravel pack around the well screen. This artificial gravel pack has in the prior practice been composed entirely of sized gravel.

A difiiculty is encountered from the use of such sized gravel, that is, gravel in which the individual particles are substantially all of the same size and free-flowing, and that is that parts of this uniformly-sized gravel pack may clog and other parts open to form channels through which the water flows with such speed as to carry surrounding fine sand in and through the gravel pack and to and through the screen. This results not only in continued withdrawal of sand after the well is developed and consequent injury to pumps and difficulty in handling the sand in the system, but also may withdraw so much sand about the well screen that sinking of the surface about the well and caving may result. Or there may be packing of sand in the gravel to diminish or cut off water fiow.

I have discovered that the defects in a gravel pack so artificially produced from sized gravel may be eliminated by feeding to the area surrounding the well-screen during the development of the well a properly graded mixture of gravel, or gravel and sand, wherein there are varied sizes of particles ranging from those small enough to pass through the openings of the screen up to quite large and coarse particles. When such a mixture of multi-sized particles is fed into the area surrounding the well-screen a gravel pack is gradually formed during the development of the well which has the advantageous characteristics of gravel packs formed by natural materials found in many water-bearing strata which comprise such a mixture of multi-sized particles ranging from those small enough to pass the screen up to a maximum larger size, and which form, when flowed into place in the development of the well, a gravel pack wherein relatively uniform slow travel of water takes place throughout all of the area of the outer part of said gravel pack. Channeling and continued sand withdrawal is avoided through the stabilized condition of the gravel pack thus produced, which condition is a natural quality of a pack which consists in graded particles, not uniformly sized, of varying sizes consisting of pieces of gravel too large to pass the openings of the screen, adjacent to the screen, and grading symmetrically outward from the screen with less uniform mixtures containing proportionately more fine gravel and sand as the distance of location away from the screen increases.

It is the object of my invention, therefore, to introduce directly into a water-bearing sand search stratum, the particles of which are nearly all so fine that they may pass the screen, a mixture of multi-sized particles of gravel from those small enough to pass the screen up to the large sized particles which may be found in natural water-bearing formations ofsayfrom thirty to fifty screen mesh up to one inlchl screen mesh.

In the practice of my process the well casing will be sunk a suitable distance into the waterbearing stratum to accommodate the length of Well screen which it is desirable to use. Material from the area of the water-bearing stratum which will surround the screen will be Withdrawn and analysis made as to its contents of fine sand and coarser particles. Where this analysis discloses that the stratum does not have suflicient coarse particles in it to provide a natural gravel pack in the development of the well, I will provide means for conveying a gravel mixture to the well screen, such as a larger casing around the well casing, or adjacent thereto a number of smaller sized casings, and in either case will have the lower end or ends thereof adjacent the top or to points along the side Walls of the well screen. I will then feed, through passageways formed in one way or another by this supplemental pipe or pipes, a mixture of gravel, or sand and gravel, embodying fine particles small enough to pass through the screen and larger particles up to a maximum size, for example, such as will pass a one inch mesh screen. While this mixture of gravel, or sand and gravel, is being fed down through these passageways I will develop the well by the usual methods, including pumping a heavy stream of Water through the well screen and discharging it from the well. In this manner sand will be withdrawn and the mixture of gravel, or sand and gravel, fed through the passageways aforesaid will take the place of the sand so withdrawn and will arrange itself about the well screen with large and small particles intermingled until a gravel pack has been formed about the screen of the same general nature and having the same favorable characteristics in use as a gravel pack which is formed naturally from coarse and fine materials in a Water-bearing stratum. When the development of the well has withdrawn all sand which will flow and this simulated natural gravel pack artificially provided has become stable so that there can be no caving or sinking of the ground about the well, the pipe or pipes for feeding the gravel mixture may then be Withdrawn, or may be left in place as desired. Additional gravel will be provided to fill the pipes, or the holes left by the pipes, to the top of the ground and the well will be fully developed with no sinking of the ground about it and. with a gravel pack as efiective and stable as it would be if formed from a proper mixture of materials occurring naturally.

In the drawing, illustrating somewhat diagrammatically means for carrying out my process,-

Fig. 1 is a fragmentary sectional elevation view somewhat diagrammatically showing a well casing and well screen in place and a surrounding tube for conveying the mixture of gravel to the Well screen in the practice of my process. Fig. 2 is a sectional plan view on line 2--2 of Fig. 1. Fig. 3 is a sectional plan view on line 3-3 of Fig. 4. Fig. 4 is a longitudinal fragmentary sectional view on line 4-4 of Fig. 3.

As illustrated, a well casing H! is sunk a suitable distance in the water-bearing stratum II. The distance in the stratum is determined from the analysis of material comprising it. Where that analysis shows that the material is all or nearly all fine sand that will pass the screen, the well screen I 2 may be set at practically any position in the vertical extent of the Water-bearing system, but usually will be set toward the bottom thereof and sealed in at the top of the well screen, as indicated by reference character 13, in the usual manner.

In the apparatus employed in the practice of my process of Figs. 1 and 2, a surrounding tube [4 is carried down about the well casing I and is of a size to leave an annular space l5 between it and the well casing Ill. The bottom l6 of the surrounding tube M may be positioned at any point along the Well screen l2, as shown in Fig. 1, and in some instances higher than the top thereof, and the mixture of gravel will thus be delivered directly to the area surrounding the screen as sand is Withdrawn from that area in pumping development of the well. The application of known methods of development will then produce from this artificially inserted mixture of gravel, or sand and gravel, a gravel pack as effective and stable as it would be if formed from a proper mixture of materials occurring naturally, In the placement of this mixture of gravel, or sand and gravel, and the accomplishment of proper development, the bottom l6 of outer casing l4 and the bottom I! of the inner casing 13 may be in any desired position with relation to each other and with the screen l2, depending upon conditions encountered, provided that it is effective in forming the gravel pack, and in general that will be with the end of the gravel-delivering passage l5 close to the screen and at the end of the process adjacent its top.

In the practice of the process as disclosed in Figs. 3 and 4, a multiplicity of smaller pipes l9 will be sunk about well casing Hi, their bottoms 20 may be positioned at any point along or above the well screen I2, being shown in Fig. 4 as coming to a point well below the top l3 of screen [2. And here again where the smaller pipes or tubes are used, the mixture of gravel, or sand and gravel, particles fed down through the tubes will be delivered directly to the area surrounding the well screen where such mixture will fill the space left by the withdrawal of sand and will ultimately form a gravel pack around the well screen similar to that which would be formed from a proper mixture of naturally placed materials formed in situ in the water-bearing stratum. In the placement of this mixture of gravel, or sand and gravel, and the accomplishment of proper development, the bottom ll of the inner casing l3 and the bottoms 20 of the surrounding smaller pipes or tubes may be in any desired position with relation to each other and with the screen l2, depending upon conditions encountered, but as with surrounding casing I4 this position must be such as will effectively place the gravel pack in position about the screen, and at the end of the process adjacent the top of the screen.

In this manner a highly effective gravel pack is formed in water-bearing strata where there are no natural materials out of which such a gravel pack could be formed, but which gravel pack thus artificially produced is made up of particles grading from such as are small enough to pass the screen to large particles such as would only pass-say-a one inch screen. Such an artificially formed gravel pack will prevent any sinking or caving of the ground about the well and will be held in position in a stable and dependable manner for long-time service, delivering water through it to the screen in a uniform and satisfactory manner.

I claim:

1. The process of forming a gravel pack about well screens which consists in sinking the well casing a requisite distance into the water-bearing stratum and setting the well screen in said stratum in the bottom of said casing, taking material of said stratum from areas about said well 1 screen and determiniggjlgerefrom th at there are insu iii ci ent ggavel particle sfifi place therein to foi m a satisfactfir'y natural gravel pack, providing gravel conveying means and sinking it through the drift to a point adjacent the top of the well screen where gravel conveyed therethrough can move to and about the walls of the well screen, developing the well by known means including pumping water and sand, feeding through said conveying means while the well is being developed a mixture of multi-sized gravel particles from those small enough to pass the screen through various larger sizes so that said fed gravel particles can move into the spaces about the well screen theretofore occupied by the withdrawn sand, and continuing such feed of multi-sized gravel particles until a gravel pack has been formed about the screen having the nature and characteristics of a gravel pack formed from multi-sized particles present in water-bearing strata.

2. The process of forming a gravel pack about well screens which consists in sinking the well casing a requisite distance into the water-bearing stratum and setting the well screen in said stratum in the bottom of said casing taking material from said stratum from areas about said well screen and determining therefrom that there are insufiicient gravel particles in place therein to form a satisfactory natural gravel pack, providing gravel conveying means and sinking it through the drift to a point adjacent the top of the well screen where gravel conveyed therethrough can move to and about the walls of the well screen, developing the well by known means including pumping water and sand, feeding through said conveying means while the well is being developed a mixture of multi-sized gravel particles from thirty to fifty mesh at-the smaller limits of size and from one mesh to four mesh at the larger limits of size, so that said fed gravel particles can move into the spaces about the well screen theretofore occupied by the withdrawn sand, and continuing such feed of multi-sized gravel particles until a gravel pack has been formed about the screen having the nature and characteristics of a gravel pack formed from multi-sized particles present in water-bearing strata.

HOWARD O. WILLIAMS.

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